Method of making an orifice



Sept. 13, 1960 F. B. BURT METHOD OF MAKING AN ORIFICE Filed Dec. 30, 1957 FARLOW 8. BUR

United States Patent METHOD OF MAKING AN ORIFICE Farlow B. Burt, South Bend, Ind., assignor to The Bendix Corporation, a corporation of Delaware Filed Dec. 30, 1957, Ser. No. 706,059

2 Claims. (Cl. 29-157) The present invention relates to an improved orifice construction; and to a method of accurately making the same.

An object of the present invention is the provision of a new and improved orifice construction which can be accurately and simply made'to meter very small fluid flows.

Another object of the invention is the provision of a new and improved orifice construction capable of insuring laminar fluid flow therethrough.

A further object of the invention is the provision of a new and improved method of readily and simply making a plurality of orifices all of which will have substantially identical flow characteristics.

Further objects and advantages of the present invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments and methods of making the same which will be described with reference to the accompanying drawing forming a part of the specification, and in which:

Figure 1 is a perspective view of a cylindrical rod having one surface milled to a uniform depth and which is cut into pieces of substantially uniform length;

Figure 2 is a cross-sectional view of a pump rotor showing one of the pieces of rod seen in Figure 1 being pressed into a flow passage of the rotor;

Figure 3 is a top end view of the rotor shown in Figure 2 having three flow passages formed by the preferred method of the present invention.

While the invention may be otherwise embodied, the orifice construction of the present invention is herein shown as embodied in a pump rotor shown and described in a copending application Serial Number 749,133, filed on July 17, 1958, and which is assigned to the assignee of the present invention. The rotor member A has a plurality of flow passages therein through which the rate of flow must be substantially identical when subjected to identical pressure differentials for reasons which will be apparent by referring to the above referred to application, and which flow passages utilize the orifices constructed according to principles of the present invention.

The flow passages or orifices that are formed in the body member A have a cross section which is a segment of a circle, and a suflicient length to at all times assure laminar flow through the passages 10. The orifice construction shown comprises three longitudinally extendingopenings 12 of substantially the same size, and which in the present instance are formed by drills of the same size, and into which plugs 14 of substantially identical cross section are pressed. The plugs 14 are made from cylindrically shaped rods having substantially the same cross section as the openings 12 which have been previously slotted or machined to remove sections of metal of substantially identical cross section. The cross section of metal removed from each of the plugs 14 may be variously shaped so long as substantially the same cross section is removed from each plug; and in the preferred embodiment shown in the drawing, the cross section of metal removed will be a segment of a circle. By means of the segmental shape of opening thus formed in the rotor member, a considerable surface area per unit length of orifice is achieved in which the side walls are closely spaced such that the film of liquid adjacent the opposing side surfaces, and in which laminar flow exists, will at all times abut each other to prevent a central core of turbulent flow from forming. Inasmuch as the orifice configuration shown in the drawing provides closely spaced sidewall surfaces, the length of the flow passage or orifice might be quite short; but inasmuch as orifices of any length can be easily made by the present invention, they will preferably have a length which exceeds the width of the orifice so that laminar flow will at all times be assured even though extreme changes in pressure drop be produced across the passages.

In the preferred method of making the orifice construction shown in the drawings, a rod of cylindrical material having a substantially uniform cross section throughout its length, and which in the present instance is a cold rolled or cold drawn rod, is placed on the bed of a machine tool, and a uniform depth of material is removed from one side thereof. The machine tool used may be of any suitable type as will occur to those skilled in the art, as for example: a grinder, a planer, shaper, or miller and in the preferred method shown in the drawing a milling machine will be utilized to plane or mill olf a generally predetermined depth of material from the top surface of a rod; and the plugs 14 are formed by cutting sections of substantially the identical length from the rod 16 after it has been milled.

In some instances, drilled holes that are otherwise unfinished may be used to receive the plugs 14; but in the arrangement shown in the drawing, the holes 12 were drilled and then reamed to provide an opening which was within .0005 of an inch of a predetermined diame ter. In the present instance the openings 12 were finished to a nominal diameter of .249 inch and the cold rolled rod 16 had a nominal diameter of .250 inch to provide an interference fit of approximately .001 of an inch. The rotor body A was placed upon the bed of a press; plug 14 was placed on the end of one of the openings 12; and the arbor 18 of the press was brought down upon the plug 14 to force it into the opening 12. While other methods of supporting the plugs 14 in the openings 12 may be utilized, the interference fit used in the preferred method of assembly, simply and inexpensively provides a fluid type joint between the plug and its opening except in the region of the segmental flow passages 10; and it is a property of this method of forming an orifice that variations in the amount of interference between the plug and its receiving opening, as brought about by the tolerances in the CD. of the plug and the ID. of the opening 12, will not appreciably change the cross-sectional area of the flow passages 10. The geometry of the segmental opening is such, that the cross-sectional area of segments of circles of slightly different radius will not vary appreciably. Where the cord of the segment is held to be a fraction of a diameter of the plug, the flat surface of the plugs 14 will be uniformly spaced from the side wall of the openings in which they are pressed so as to provide openings having substantially identical cross-sectional area.

While the invention has been set forth in considerable detail, I do not wish to be limited to the particular constructions shown and described; it is my intention to cover hereby all novel adaptations, modifications, and arrangements thereof which come within the practice of those skilled in art to which the invention relates.

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